I'm not going to be a lot of help, but I do have a mutt ai2 one size diaper, and I love it so far. I just started using it on my 1 year old who is 22 lbs. She's already on the highest rise, though, and she's a short girl. She does still have room to grow in the waist. I don't know that it will last her until she pl's, but at least for now we like it a lot. And hopefully if we have another child, he or she will be able to use it. I've never tried the SOS so I can't comment on that.